Some like it hot and cold

7th March 2011
ES Admin

Especially the new PowerlinePLUS-Converters. They provide 20 to 50 watts and have been designed for applications with a temperature range of -55°C and 100°C.­ Converters with theses specifications are focussed to railway applications, aerospace, traffic controls, wind energy and semi military environments. They are however also ideal for industrial applications, in which heat generation has to be reduced.

The RPP-family can be supplied with a heat sink with cooling fins, or with a flat surface plate for case mounting. For the heat-sink version cooling fins ensure optimal heat dissipation – the flat surface version relies on the heat transfer to the case.

Power loss reduced by 15 to 20%

The ICE-technology, specially developed for the PowerlinePLUS-family enhances the efficiency by more than 2% up to 92%.This reduction which does not seem substantial reduces however within the converter the power loss by 15 to 20% Furthermore the efficiency of the converter is fairly constant for the total input voltage range, quite contrary to conventional converters. Standard converters are designed to to achieve their max. efficiency at 25°C, full load and rated voltage. Operation with reduced load and increased operating temperature considerably reduces efficiency.

Two case variants provide optimized cooling

The internal design of these converters ensures that “hot” components are in direct contact with converter case. This is especially so for the switching-FETs, the transformer and the synchronous rectifiers. The case is laid out as a six sided shield.The base material is hardened/re-inforced aluminium derived from the arcraft industry, which features excellent heat conductivity.The surface features either cooling fins for convection cooling, or a flat base plate for direct case mounting.The base plate is also made of high grade aluminium and together with substantial mounting pins provides additional cooling.This contruction concept is of course more intricate, reduces however the internal thermal impedance considerably.

For applications with ambient temperatures from -55°C to 100°C

A key design feature is the selection of temperature stable components – including the material of the printed circuit board. The weakest link always determines the quality of a design. Only “high-grade temperature” components are used in the design of the PowerlinePLUS-family. This is particularly so for the transformer core – singular overheating can already lead to a loss of magnetism of the transformer core. Transformers of the PowerlinePLUS-family operate at case temperatures beyond 115°C without problem and ensure that these converters do not require “derating” or additional cooling at an ambient operating temperature of 100°C. An internal thermistor circuit protects the converter should the maximum operating conditions be exceeded for prolonged periods.

Low temperatures also pose problems. They can be of a mechanical nature, as differing temperature coefficients of the pcb and the components can cause material failures. The temperature sensitivity of bi-polar transistors in the feed-back- and oscillator circuit can cause start- up problems of the converter at very low temperatures. A special circuit ensures that the PowerlinePLUS-family starts-up even at -55°C without problems- without negatives for the efficiency, as would be the case with a simply increased bias-current.

Input voltage up to 160V, high isolation, internal filter

RPP-converters are supplied with a standard 2:1 input(e.g.9V – 18V) or with a wide 4:1 input( 18V – 72V) ratio. A” class – B” – filter is standard. Inputs and outputs are fully protected against electrical and thermal overloads – the isolation ranges up to 2,25kV resp. 3kV.

Prices are very attractive and are considerably lower than comparable “High-end”-products. A price comparison with standard converters is also favourable, based on the possibility of using a lower power rating due to the obsolescence of a “de-rating” up to 100°C.

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